Power generation control system for fuel cell

ABSTRACT

A power generation control system which includes: a fuel cell ( 201 ); a target power provider ( 101 ) for the fuel cell ( 201 ); a operation status monitoring system ( 102 ) for monitoring output power from the fuel cell ( 201 ), in which the detected output power includes actual output voltage (AV) of the fuel cell ( 201 ); and a controller ( 214 ). The controller ( 214 ) includes: a target current computing unit ( 104 ) which calculates a target current (TI) from the target power (TPW) given by the target power provider ( 101 ), based on PW-I characteristic obtained from I-V characteristic of the fuel cell ( 201 ); and a command output power computing unit ( 106 ) which calculates a command output power (CPW) of the fuel cell ( 201 ) based on the target current (TI) and the actual output voltage (AV).

TECHNICAL FIELD

The present invention relates to a power generation control system for afuel cell, which provides power generation thereof adjusted to thechanging output characteristics thereof.

BACKGROUND ART

In a fuel cell system of a fuel-cell vehicle, output of a fuel cellthereof is controlled based on instructions from a vehicle controlsystem.

While the fuel cell system is in warm-up right after the start-upthereof, or due to the deterioration of the system with age, the outputcharacteristics of the fuel cell thereof change to have a lower outputvoltage. In order to obtain the required output power from the fuel cellat the lower output voltage, an operation point (output current andoutput voltage) of the fuel cell is shifted to have the output currentincreased to thereby compensate for shortage of the output power.However, under heavy load conditions at a relatively high outputcurrent, the output voltage sharply drops with increasing outputcurrent, which further decreases the output power. The system controlsto have the output current further increased in order to gain the outputpower. This brings about a further drop in the output voltage, andconsequently in this vicious circle, the required output power cannot beobtained.

Japanese Patent Application Laid-open No. 2002-231295 discloses a powercontrol system in which an output characteristic of the fuel cell iscorrected based on actual output current and voltage thereof, and anoperation point is adjusted based on the corrected outputcharacteristic.

DISCLOSURE OF INVENTION

In the above control system, however, the operation point of the fuelcell is preset based on the corrected output characteristic. Therefore,if the corrected output characteristic is different from the actualoutput characteristic thereof, the system may fall into theabove-mentioned vicious circle which brings harsh operating conditionsto the fuel cell causing accelerated deterioration thereof, failing toobtain the required output power from the fuel cell.

The present invention was made in the light of this problem. An objectof the present invention is to provide a power generation control systemfor a fuel cell, which ensures sufficient output power of the fuel celland prevents deterioration thereof, coping with the changingoutput-characteristic thereof.

An aspect of the present invention is a power generation control systemcomprising: a fuel cell for generating power from fuel gas and oxidantgas fed thereto; a target power provider for providing a target powerfor the fuel cell; a detector for detecting output power from the fuelcell, the detected output power including actual output voltage of thefuel cell; and a controller comprising a target current computing unitwhich calculates a target current from the target power based on apower-current characteristic obtained from the output characteristic ofthe fuel cell, and a command output power computing unit whichcalculates a command output power of the fuel cell based on the targetcurrent and the actual output voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to the accompanyingdrawings wherein:

FIG. 1 is a diagram showing a configuration of a power generationcontrol system for a fuel cell according to the first embodiment of thepresent invention;

FIG. 2 is a diagram showing a configuration of a fuel cell system thatincludes the power generation control system of FIG. 1;

FIG. 3 is a graph showing an output characteristic (i.e., acharacteristic curve showing a relationship between output current andoutput voltage, hereinafter referred to as I-V characteristic) of thefuel cell according to the first embodiment;

FIG. 4 is a diagram showing a configuration of a power generationcontrol system for a fuel cell according to the second embodiment of thepresent invention;

FIG. 5 is a flowchart showing a process of controlling power generationof the fuel cell according to the second embodiment;

FIG. 6 is a flowchart showing a learning process of the I-Vcharacteristic of the fuel cell according to the second embodiment;

FIG. 7 is a flowchart showing a process of calculating target power TPW[W] according to the second embodiment;

FIG. 8 is a flowchart showing a process of calculating target current TIaccording to the second embodiment;

FIG. 9 is a flowchart showing a process of calculating target gasoperation point according to the second embodiment;

FIG. 10 is a graph showing the I-V characteristic of the fuel cellaccording to the second embodiment;

FIG. 11 is a diagram showing a configuration of a power generationcontrol system for a fuel cell according to the third embodiment of thepresent invention;

FIG. 12 is a flowchart showing a process of calculating target currentTI according to the third embodiment;

FIG. 13 is a flowchart showing a process of calculating target gasoperation point according to the third embodiment; and

FIG. 14 is a flowchart showing a learning process of the I-Vcharacteristic of the fuel cell according to the fourth embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be explained below withreference to the drawings, wherein like members are designated by likereference characters.

A power generation control system S1 according to the first embodimentshown in FIG. 1 comprises a target power provider 101, an operationstatus monitoring system 102, a target current computing unit 104, atarget gas operation point computing unit 105, an command output powercomputing unit 106, a gas control system 107, and a power extractioncontroller 108.

The target power provider 101 calculates a target power TPW to providethe system S1 therewith. In the present control system S1 applied to afuel-cell vehicle, the target power provider 101 is provided in avehicle control system VCS, in which the target power TPW is calculatedbased on the driver's demand and characteristics of the vehicle.

The operation status monitoring system 102 monitors the operation statusof the fuel cell by detecting an actual output voltage AV thereof.

The target current computing unit 104 calculates a target current TIfrom the target power TPW provided by the target power provider 101,based on a power-current characteristic (hereinafter referred to as PW-Icharacteristic) which can be obtained from a nominal I-V characteristic(i.e., reference I-V characteristic) of the fuel cell.

Based on the target current TI calculated by the target currentcomputing unit 104, the target gas operation point computing unit 105calculates a target gas pressure TPR and a target gas flow rate TQ atthe target operation point of fuel gas and oxidant gas supplied to thefuel cell. Although only the target gas pressure TPR is illustrated inFIG. 1, in the target gas operation point computing unit 105, the targetgas flow rate TQ is also included therein.

The command output power computing unit 106 calculates command outputpower CPW for power generation of the fuel cell, based on the actualoutput voltage AV detected by the operation status monitoring system 102and the target current TI calculated by the target current computingunit 104.

The gas control system 107 controls supply of the fuel gas and theoxidant gas to the fuel cell, based on the target gas operation point(the target gas pressure TPR and the target gas flow rate TQ) calculatedby the target gas operation point computing unit 105, and an actual gaspressure APR and an actual gas flow rate AQ to be described later.

The power extraction controller 108 controls power extraction from thefuel cell, based on the command output power CPW for power generationthereof calculated by the command output power computing unit 106.

FIG. 2 is a diagram showing a configuration of a fuel cell system FCSthat includes the power generation control system S1 according to thefirst embodiment. in FIG. 2, the fuel cell system FCS comprises a fuelcell stack 201, a hydrogen gas feed system Sh which feeds hydrogen gasas fuel gas to the fuel cell stack 201, an air feed system Sa whichfeeds air as oxidant gas to the fuel cell stack 201, a humidificationsystem Sw which humidifies hydrogen gas and air upstream of the fuelcell stack 201, a drive unit 209 which extracts the power generated bythe fuel cell stack 201, and a controller 214.

The humidification system Sw has a humidifier 202, and a deionized waterpump 207 which supplies deionized water for humidification to thehumidifier 202.

The air feed system Sa comprises a compressor 203 which introduces airto the system, a throttle valve 205 which discharges air from the fuelcell stack 201 to the outside of the system, in which the compressor 203and throttle valve 205 are operated to control air pressure Pa and airflow rate Qa in the system, an air pressure sensor 210 which detects airpressure Pa at an inlet of the fuel cell stack 201, and an air flowmeter212 which measures flow rate Qa of air flowing into the fuel cell stack201.

The hydrogen gas feed system Sh comprises a high-pressure gas tank 204 awhich stores hydrogen gas therein, a variable throttle regulator 204which controls flow rate of the hydrogen gas, an ejector 208 which pumpsunused hydrogen gas from the fuel cell stack 201 to the upstream thereoffor recirculation, a purge valve 206 which discharges hydrogen gas tothe outside of the system, a hydrogen gas pressure sensor 211 whichdetects hydrogen pressure Ph at the inlet of the fuel cell stack 201,and a hydrogen gas flowmeter 213 which measures flow rate Qh of hydrogengas flowing into the fuel cell stack 201.

On an electrical wiring line from the fuel cell stack 201 to the driveunit 209, a voltmeter 215 and an ammeter 216 are provided, whichrespectively measure the actual voltage AV and actual current AI of theoutput power of the fuel cell stack 201.

In the air feed system Sa, the air is introduced into the system andcompressed by the compressor 203, and properly humidified through thehumidifier 202 to be fed to the fuel cell stack 201. In the hydrogen gasfeed system Sh, the hydrogen gas is supplied from the high-pressure tank204 a to the system, at the pressure and flow rate thereof regulated bythe regulator 204. The hydrogen gas meets at the ejector 208 with therecirculated hydrogen gas and is properly humidified through thehumidifier 202 similarly in the air feed system Sa to be fed to the fuelcell stack 201.

In the fuel cell stack 201, oxygen and hydrogen respectively containedin the air and hydrogen gas fed thereto electrochemically react witheach other to generate electric power. Generated power (i.e., current)is supplied to the external system in the vehicle. The air unused forpower generation in the fuel cell stack 201 is discharged to theatmosphere via the throttle valve 205. The hydrogen gas from the fuelcell stack 201, which is unused for the power generation, is introducedby the ejector 208 to a supply line upstream of the humidifier 202 to bereused for power generation.

The controller 214 reads the detection values obtained from the airpressure sensor 210, the air flowmeter 212, the hydrogen gas pressuresensor 211, the hydrogen gas flowmeter 213, the voltmeter 215, and theammeter 216. After reading the detection values from these sensors, thecontroller 214 determines the target current TI based on the targetpower TPW, and based on the target current TI, the controller 214determines target control values for controlling the compressor 203, thethrottle valve 205 and the regulator 204. Further, the controller 214determines an output current to be extracted from the fuel cell stack201 to the drive unit 209 based on the actual gas pressure and gas flowrate obtained from the above-described sensors, and gives the outputcurrent as the command output power CPW to the drive unit 209.

The components of the fuel cell system FCS shown in FIG. 2 and thecomponents of the power generation control system S1 shown in FIG. 1have the following relationships. The voltmeter 215 corresponds to theoperation status monitoring system 102. The controller 214 includes thetarget current computing unit 104, the target gas operation pointcomputing unit 105, and the command output power computing unit 106. Thecompressor 203, the regulator 204, and the throttle valve 205 areincluded in the gas control system 107. The drive unit 209 correspondsto the power extraction controller 108.

FIG. 3 is a graph showing nominal I-V characteristic (1) of a fuel cellin good condition with low operating hours, and I-V characteristic (2)of the fuel cell with the performance thereof degraded due todeterioration with age or insufficient warm-up.

In the case where the target gas operation point is determined based onthe target power TPW required from the vehicle control system VCS, andthe target power TPW is set as the command output power CPW, the outputpower extracted from the fuel cell is controlled to be at an outputcurrent I0 which is equal to the target current TI, assuming that theperformance of the fuel cell exhibits the nominal I-V characteristic.However, the actual I-V characteristic of the fuel cell may deviate fromthe nominal I-V characteristic (1) and change to the curve (2) due todeterioration with age or insufficient warm-up. The output voltage atthe output current I0 drops from V0 to V1, and therefore only a outputpower PW1 that is smaller than the target power TPW can be extractedfrom the fuel cell.

As the command output power CPW is set to the target power TPW, theoutput current is controlled to increase from I0 to I1′ in order to havethe product of the detected voltage AV and current AI reach the targetpower TPW. During this period, the target values of the pressure andflow rate of the respective hydrogen gas and air (i.e., the target gasoperation point) are set to the values calculated based on the targetpower TPW (at the current I0) which derives from the nominal I-Vcharacteristic.

However, the I-V characteristic (2) of the fuel cell has a tendencythat, in a region of the heavy-load condition at a greater outputcurrent near the output current I1, the output voltage sharply dropswith increasing output current.

Therefore, if the output current increases from I0 to I1′, the outputvoltage drops from V1 to V1′ to provide an output power PW1′ lower thanPW1. Accordingly, the target power TPW cannot be extracted from the fuelcell. While the system further controls to increase the output currentfrom I1′ to I1″, the voltage sharply drops from V1′ to V1″, as can beseen from the I-V characteristic (2). As a result, the output powerfurther decreases to PW1″ that is lower than PW1′, and the desiredtarget power TPW cannot be extracted. Moreover, the extraction of suchan excess current has a risk of affecting a polymer electrolyte film ofthe fuel cell.

On the other hand, according to the first embodiment, when the vehiclecontrol system VCS requires the target power TPW, the target currentcomputing unit 104 calculates the target current TI based on the nominalI-V characteristic of the fuel cell. Then, the command output powercomputing unit 106 calculates the command output power CPW from aproduct (TI×AV) of the target current TI and the actual voltage AV ofthe fuel cell stack 201.

With the above configuration, when the output current I0 equal to thetarget current TI is extracted from the fuel cell, the command outputpower CPW is set to the power PW1 that is equal to the product (TI×AV)of the target current TI and the actual voltage AV. Therefore, theoperation point of the fuel cell lies on the I-V characteristic (2).This prevents the unlimited increase of the output current from I0 toI1′ and from I1′ to I1″ for extraction of the target power TPW, thusprotecting the polymer electrolyte film of the fuel cell from excesscurrent extraction.

As explained above, according to the first embodiment, the commandoutput power CPW is based on the product of the target current TIcalculated from the target power TPW and the actual voltage AV of thefuel cell. Therefore, even if the I-V characteristic of the fuel cellchanges due to deterioration with age or insufficient warm-up,adjustment of the command output power CPW can follow the changingactual I-V characteristic. Accordingly, even if the actual output powerdoes not reach the target power TPW, the system does not fall in avicious cycle, in which increase of the output current for compensatingfor shortage of the output power leads to the output voltage drop,further lowering the output power. Consequently, the actual output powerof the fuel cell follows the command output power CPW for powergeneration thereof, whereby the deterioration thereof can be prevented.

FIG. 4 is a diagram showing a configuration of a power generationcontrol system S2 for a fuel cell according to the second embodiment ofthe present invention. The power generation control system S2 includesan I-V characteristic learning unit 103 in addition to the components ofthe power generation control system S1 shown in FIG. 1.

The operation status monitoring system 102 detects the actual outputcurrent AI of the fuel cell in addition to the actual output voltage AVthereof for monitoring the operation status of the fuel cell.

The I-V characteristic learning unit 103 learns the actual I-Vcharacteristic of the fuel cell from the actual voltage AV and theactual current AI thereof detected by the operation status monitoringsystem 102, and corrects the I-V characteristic thereof. The learned andcorrected I-V characteristic is given to the target current computingunit 104.

The target current computing unit 104 obtains the PW-I characteristicbased on the I-V characteristic given from the I-V characteristiclearning unit 103, and calculates the target current TI based on thePW-I characteristic.

Configurations of other components are similar to those shown in FIG. 1.Corresponding relationships between the components of the powergeneration control system S2 for a fuel cell shown in FIG. 4 and thecomponents of the fuel cell system FCS shown in FIG. 2 are similar tothose explained in the first embodiment. In other words, the voltmeter215 and the ammeter 216 are included in the operation status monitoringsystem 102. The controller 214 includes the I-V characteristic learningunit 103, the target current computing unit 104, the target gasoperation point computing unit 105, and the command output powercomputing unit 106. The compressor 203, the regulator 204, and thethrottle valve 205 are included in the gas control system 107. The driveunit 209 corresponds to the power extraction controller 108.

The control process performed in the power generation control system S2of the second embodiment will be explained with reference to FIG. 5 toFIG. 9.

FIG. 5 is a flowchart showing a process of controlling power generationextracted from the fuel cell.

At step S501, the target power TPW is calculated. At step S502, thetarget current TI is calculated from the calculated target power TPWbased on the PW-I characteristic which can be obtained from the nominalI-V characteristic. At step S503, the target operation points (i.e., thetarget gas pressures TPR, and the target gas flow rates TQ) of therespective fuel gas and oxidant gas supplied to the fuel cell arecalculated based on the target current TI. At step S504, the supplypressure and flow rate of the fuel gas and the oxidant gas to the fuelcell are controlled based on the calculated target gas operation point,the actual gas pressures APR, and the actual gas flow rates AQ thereof.At step S505, the actual voltage AV of the fuel cell stack 201 ismeasured. At step S506, the target current TI and the actual voltage AVare multiplied together to obtain the command output power CPW (=TI×AV).At step S507, the output power of the fuel cell is controlled based onthe calculated command output power CPW. The above process is executedat every predetermined period (for example, at every 10 ms).

FIG. 6 is a flowchart showing a learning process of the I-Vcharacteristic of the fuel cell. The process shown in FIG. 6 is executedat every predetermined period (for example, at every 10 ms) similar tothe process shown in FIG. 5.

At step S601, it is determined whether data of the actual voltage AV andthe actual current AI of the fuel cell stack 201 is readable (that is,whether the operation of the fuel cell is not in a transient state wherethe operational data thereof fluctuate too widely to acquire). When itis determined that the data is readable, the process proceeds to stepS602. When it is determined that the data is not readable, the processproceeds to step S604. At step S602, the actual voltage AV and theactual current AI of the fuel cell stack 201 are measured. At step S603,the values measured at step S602 are stored into the memory.

At step S604, it is determined whether the number of data stored at stepS603 exceeds a predetermined number α (for example, 5000). When thenumber exceeds the predetermined number α, the process proceeds to stepS605. When the number does not exceed the predetermined number α, thisoperation routine ends. At step S605, it is determined whether theelapsed time from a start of the data collection or the learning timeexceeds a predetermined time β (for example, three hours). When it isdetermined that the learning time exceeds the predetermined time β, theprocess proceeds to step S606. On the other hand, when it is determinedthat the learning time does not exceed the predetermined time β, theoperation routine ends. Lastly, at step S606, the collected and storedactual voltages AV and actual currents AI are respectively averaged toobtain learning data IV1. This learning data IV1 is stored into apredetermined memory variable as data IV that represents the currentactual I-V characteristic, and the operation ends.

FIG. 7 is a flowchart showing a process of calculating the target powerTPW at step S501 shown in FIG. 5.

At step S701, it is determined whether power consumption data ofauxiliary equipment for power generation of the fuel cell system FCS isto be updated, wherein, when the I-V characteristic is updated, theauxiliary equipment consumption data is updated. When it is determinedat step S701 that the auxiliary equipment consumption data is updated,the process proceeds to step S702. On the other hand, when it isdetermined at step S701 that the auxiliary equipment consumption data isnot updated, the process proceeds to step S706.

At step S702, the latest I-V characteristic is read. At step S703, agross power Pwgross is calculated as the product of the output currentand the output voltage at a point on the read latest I-V characteristiccurve, and PWgross-I characteristic is created, which representrelationship between the gross power PWgross and the output current. Atstep S704, auxiliary equipment power consumption PWaux for variouscurrents are first calculated from the gas pressures and gas flow rates(i.e., the operation point) of the fuel gas and oxidant gas required forgenerating predetermined currents, and PWgross-PWaux characteristic iscreated, which represent a relationship between the auxiliary equipmentpower consumption PWaux and the gross power PWgross. At step S705, netpower PWnet is obtained by subtracting the auxiliary equipment powerconsumption PWaux from the gross power Pwgross (PWnet=PWgross−PWaux) ata point on the PWgross−PWaux characteristic curve, and PWnet−PWauxcharacteristic is created, which represent a relationship between thenet power PWnet and the auxiliary equipment power consumption PWaux.Then, the data stored in the memory is updated according to the createdPWnet−PWaux characteristic.

At step S706, target net power TPWnet that is required from the vehiclecontrol system VCS is read. At step S707, target auxiliary equipmentpower consumption TPWaux is calculated from the target net power TPWnetbased on the PWnet-PWaux characteristic updated at step S705. Lastly, atstep S708, the target net power TPWnet and the target auxiliaryequipment power consumption TPWaux are added to obtain target gross poerTPWgross (=TPWnet+TPWaux), and the routine ends.

FIG. 8 is a flowchart showing a process of calculating the targetcurrent TI at step S502 shown in FIG. 5.

At step S801, the learned latest I-V characteristic is read. At stepS802, gross power PWgross is calculated as the product of the outputcurrent and the output voltage at a point on the read latest I-Vcharacteristic curve, and PWgross-I characteristic is computed, whichrepresent a relationship between the gross power PWgross and the outputcurrent. At step S803, the target gross poer TPWgross is read. At stepS804, the target current TI is calculated from the target gross poerTPWgross based on the PWgross-I characteristic, and the routine ends.

FIG. 9 is a flowchart showing a process of calculating the target gasoperation point at step S503 shown in FIG. 5.

At step S901, the target current TI obtained in the processing at stepS502 shown in FIG. 5 is read. At step S902, the target gas pressure TPRand a target air flow rate TQair are calculated from the target currentTI based on gas operation point calculation data prepared in advance,and the routine ends.

In the first embodiment according to the present invention, the increasein the output current in a vicious cycle from I0 to I1′ and from I1′ toI1″ can be prevented, since the product of the target current TI and theactual voltage AV is set as the command output power CPW. However, insuch a case, only the actual power PW1 that is smaller than therequested target power TPW can be extracted from the fuel cell.

In the second embodiment, the actual I-V characteristic changing due tothe insufficient warm-up or deterioration with age is learned throughmeasurement of the actual voltage AV and the actual current AI of thefuel cell. The PW-I characteristic is computed based on the learned I-Vcharacteristic, and based on the PW-I characteristic, the target currentTI is obtained from the target power TPW given from the vehicle controlsystem VCS. In other words, the I-V characteristic as the basis forobtaining the target current TI is different between the first andsecond embodiments, resulting in the different target currents TIcalculated from the same target power TPW.

For example, if I-V characteristic of the fuel cell is learned to be asthe curve of the I-V characteristic (3) shown in FIG. 10, an outputcurrent I2′ at a point thereon achieving the required target power TPW,which is a intersection between the curve of the I-V characteristic (3)and a curve representing the generated power of PW2′, is determined asthe target current TI. This output current I2′ is greater than theoutput current I0 of the operation point of the fuel cell according tothe first embodiment. Therefore, the target gas operation point iscontrolled and shifted based on the current I2′ to have greater targetgas pressure TPR and target gas flow rate TQ thereof than the valuesobtained based on the current I0. Accordingly, regarding the I-Vcharacteristic (3), a sharp voltage drop under the heavy load conditionis prevented.

The command output power CPW is then obtained as the product of thecurrent I2′ and the voltage V2′ which is the actual output voltage AV,whereby the actual output power of the fuel cell becomes substantiallyequal to the required target power TPW.

As explained above, in the second embodiment, even when the I-Vcharacteristic of the fuel cell changes due to deterioration with age orinsufficient warm-up, the excess current extraction in the vicious cyclecan be prevented, and the output power can be substantially equal to thetarget power. These effects are obtained in addition to those obtainedfrom the first embodiment.

Further, the actual current AI and the actual voltage AV are monitoredduring the operation of the fuel cell with data of which arecontinuously collected. The actual I-V characteristic of the fuel cellis thus learned and corrected based on the collected actual current AIand actual voltage AV, whereby precise system control can be achieved.

Further, the target power TPW is calculated, taking into account thepower consumed by the auxiliary equipment associated with the systempower generation. The power consumption characteristic of the auxiliaryequipment (i.e., the auxiliary equipment consumption data) is alsocorrected when the I-V characteristic and the PW-I characteristic arecorrected through the learning process. Therefore, even when the powerconsumption of the auxiliary equipment changes due to the correction ofthe I-V characteristic and the PW-I characteristic, desired target powerTPW can be achieved.

FIG. 11 is a diagram showing a configuration of the power generationcontrol system S3 for a fuel cell according to the third embodiment ofthe present invention. The target current computing unit 104 in thesecond embodiment obtains the PW-I characteristic based on the I-Vcharacteristic learned and corrected by the I-V characteristic learningunit 103. In the third embodiment, the target gas operation pointcomputing unit 105 calculates the target gas operation point based onthe I-V characteristic learned and corrected by the I-V characteristiclearning unit 103. The target current computing unit 104 has aconfiguration similar to that in the first embodiment.

The target gas operation point computing unit 105 calculates the targetgas operation point (i.e., the target gas pressure TPR, and the targetgas flow rate TQ) based on the target current TI obtained by the targetcurrent computing unit 104 and the I-V characteristic learned andcorrected by the I-V characteristic learning unit 103.

Configurations of other components are similar to those shown in FIG. 1and FIG. 2. Relationships between the components of the power generationcontrol system S3 for a fuel cell shown in FIG. 11 and the components ofthe fuel cell system FCS shown in FIG. 2 are similar to those explainedin the first and the second embodiments. In other words, the voltmeter215 and the ammeter 216 are included in the operation status monitoringsystem 102. The controller 214 includes the I-V characteristic learningunit 103, the target current computing unit 104, the target gasoperation point computing unit 105, and the command output powercomputing unit 106. The compressor 203, the regulator 204, and thethrottle valve 205 are included in the gas control system 107. The driveunit 209 corresponds to the power extraction controller 108.

The control process performed in the power generation control system S3of the third embodiment will be explained with reference to FIG. 12 toFIG. 13. The process of the output power extraction from the fuel cell,the process of learning the I-V characteristic thereof, and the processof calculating the target power TPW are similar to those shown in therespective flowcharts of FIG. 5, FIG. 6, and FIG. 7. Explanationsthereof are therefore omitted.

FIG. 12 is a flowchart showing the process of calculating the targetcurrent TI at step S502 shown in FIG. 5.

At step S1201, the target gross power TPWgross is read. At step S1202,the target current TI is calculated from the target gross power TPWgrossbased on the TPW gross-I characteristic prepared in advance, then theroutine ends.

FIG. 13 is a flowchart showing a process of calculating the target gasoperation point at step S503 shown in FIG. 5.

In FIG. 13, at step S1301, the latest I-V characteristic learned andcorrected by the I-V characteristic learning unit 103 is read. At stepS1302, the reference I-V characteristic equivalent to the nominal I-Vcharacteristic shown in FIG. 3 and FIG. 10 are read. At step S1303, anI-V characteristic deviation ratio S which represents how much thelatest I-V characteristic deviates from the reference I-V characteristicis calculated, for example, as follows:S(i)=IV(i)/IVleaned(i),S=ΣS(i)/N,

wherein i represents an integer from 1 to N, IV(i) represents data ateach of N points on the reference I-V characteristic curve, andIVlearned(i) represents data at each of N points on the learned I-Vcharacteristic curve at the same current values as those of the N pointsof IV(i) on the reference I-V characteristic curve. S(i)s are thuscalculated for N points in the I-V characteristic. The deviation ratio Sis then calculated as an average of N S(i)s.

At step S1304, based on the calculated deviation ratio S and referencetarget gas pressure data mPR0, a target gas pressure mPR is corrected asthe product of the target gas pressure data mPR0 and f(S)(mPR=mPR0×f(S)).

The f(S) represents a predetermined monotone increasing function whichreturns a positive value for the given deviation ratio S. Instead of thefunction f(S), table data may be used, in which positive numbers areprovided for each of various possible deviation ratios S.

At step S1305, the target current TI obtained by calculation at stepS1202 shown in FIG. 12 is read. Lastly, at step S1306, the target gaspressure TPR is calculated based on the target gas pressure mPR obtainedat step S1304. The target air flow rate TQair is calculated frompredetermined data prepared in advance, and the routine ends.

In the first embodiment of the present invention, the increase in theoutput current in a vicious cycle from I0 to I1′ and from I1′ to I1″ canbe prevented, since the product of the target current TI and the actualvoltage AV is set as the command output power CPW. However, in such acase, only the actual power PW1 that is smaller than the requestedtarget power TPW can be extracted from the fuel cell.

In the third embodiment, the actual I-V characteristic which has changeddue to insufficient warm-up or deterioration with age is learned andcorrected based on the monitored actual voltage AV and actual current AIof the fuel cell, and the target gas operation point is calculated basedon the corrected I-V characteristic. The target current TI is obtainedfrom the target power TPW given from the vehicle control system VCS,based on the nominal I-V characteristic in a similar manner to that inthe first embodiment. Therefore, for example, the output current iscontrolled to be I0 as shown in FIG. 10.

The target gas operation point is calculated based on the obtainedcurrent I0. When it is learned that the I-V characteristic of the fuelcell has deteriorated with the voltage thereof lowered, the target gasoperation point is corrected to increase the gas pressure, whereby theI-V characteristic thereof changes to recover the voltage. In otherwords, by increasing the gas pressure, the I-V characteristic of thefuel cell comes close to the nominal the I-V characteristic (1) shown inFIG. 10, whereby the output voltage of V0 can be obtained from the fuelcell at the output current I0. Consequently, the command output powerCPW calculated as the product of the actual current AI which is equal toI0 and the actual voltage AV which is equal to V0, becomes equal to thedesired target power TPW.

There is a limit to the rise in the output voltage of the fuel cellrealized by increasing the gas pressure. Therefore, when a large voltagedrop in the I-V characteristic of the fuel cell occurs, theconfiguration according to the second embodiment may preferably beemployed together with the configuration of the third embodiment.

As explained above, in the third embodiment, even when the I-Vcharacteristic of the fuel cell changes due to deterioration with age orinsufficient warm-up, a vicious cycle of excess current extraction canbe prevented, and the output power can be substantially equal to thetarget power. These effects are obtained in addition to those obtainedfrom the first embodiment.

Further, the actual current AI and the actual voltage AV are monitoredduring the operation of the fuel cell with data of which arecontinuously collected. The actual I-V characteristic of the fuel cellis thus learned and corrected based on the collected actual current AIand actual voltage AV, whereby precise and proper system control can beachieved.

Further, the target power TPW is calculated, taking into account thepower consumed by the auxiliary equipment associated with the systempower generation. The power consumption characteristic of the auxiliaryequipment (i.e., the auxiliary equipment consumption data) is alsocorrected when the I-V characteristic and the PW-I characteristic arecorrected through the learning process. Therefore, even when the powerconsumption of the auxiliary equipment changes due to the correction ofthe I-V characteristic and the PW-I characteristic, desired target powerTPW can be achieved.

A power generation control system 4 according to the fourth embodimentof the present invention will be explained next.

In the fourth embodiment, the I-V characteristic learning unit 103according to the second and the third embodiments learns and correctsthe I-V characteristic using a small amount of data collected during arelatively short period of time such as a warm-up period. Otherconfigurations are similar to those in the second or the thirdembodiment.

A learning process of the I-V characteristic learning unit 103 will beexplained with reference to a flowchart shown in FIG. 14. The learningprocess is executed at every predetermined time, for example, at every10 ms, similarly to the process shown in the flowchart in FIG. 5.

At step S1401, it is determined whether data of the actual voltage AVand the actual current AI of the fuel cell stack 201 is readable (thatis, whether the operation of the fuel cell is not in a transient statewhere the operational data thereof fluctuate too widely to acquire).When it is determined that the data is readable, the process proceeds tostep S1402. When it is determined that the data is not readable, theprocess proceeds to step S1404. At step S1402, the actual voltage AV andthe actual current AI of the fuel cell stack 201 are measured. At stepS1403, the values measured at step S1402 are stored into the memory.

At step S1404, it is determined whether the number of data stored in thememory exceeds a predetermined number γ, 10, for example. When thenumber of data exceeds the predetermined number, the process proceeds tostep S1405. When the number of data does not exceed the predeterminednumber, the learning process ends. At step S1405, an I-V characteristiccorrection factor R is calculated as follows:R(i)=IV2(i)/IV(i),R=ΣR(i)/M,

wherein i represents an integer from 1 to M, IV2(i) represents data IV2at each of M points on the curve of the learned I-V characteristicstored in the memory derived from the collected actual voltages AV andactual currents AI, and IV(i) represents data IV at each of M points onthe curve of the nominal I-V characteristic having the same currentvalues as those of M points of IV2. R(i)s are thus calculated for Mpoints in the I-V characteristic. The correction factor R is thencalculated as an average of M R(i)s.

At step S1406, the correction factor R is multiplied by the data IV0 ofthe reference I-V characteristic equivalent to the nominal I-Vcharacteristic shown in FIG. 3 and FIG. 4, to thereby revise the data IVof the learned I-V characteristic (i.e., IV=IV0×R), then the routineends.

As explained above, in the fourth embodiment, the I-V characteristic ofthe fuel cell can be learned in a shorter time than that of the secondembodiment, by correcting the basic I-V characteristic based on a smallamount of measured actual currents AI and actual voltages AV.

In the second, the third and the fourth embodiments, the I-Vcharacteristic learning unit 103 may learn and correct the I-Vcharacteristic of the fuel cell based on an actual temperature of thefuel cell measured by a temperature sensor or thermometer 217 and aplurality of pieces of I-V characteristic data prepared for various fuelcell temperatures. With this configuration, even when the temperature ofthe fuel cell changes, the learned I-V characteristic thereof can bemore accurate, whereby the control of power generation thereof can beachieved with enhanced precision.

The present disclosure relates to subject matter contained in JapanesePatent Application No. 2002-374433, filed on Dec. 25, 2002, thedisclosure of which is expressly incorporated herein by reference in itsentirety.

The preferred embodiments described herein are illustrative and notrestrictive, and the invention may be practiced or embodied in otherways without departing from the spirit or essential character thereof.The scope of the invention being indicated by the claims, and allvariations which come within the meaning of claims are intended to beembraced herein.

INDUSTRIAL APPLICABILITY

In the power generation control system for a fuel cell according to thepresent invention, the target current computing unit 104 calculates atarget current from a target power, which is given by the target powerprovider 101, based on the power-current characteristic (PW-Icharacteristic) obtained from the output characteristic (I-Vcharacteristic) of the fuel cell. The command output power computingunit 106 calculates the command output power of the fuel cell based onthe target current and the actual voltage of the fuel cell measured bythe operation status monitoring system 102. This configuration ensuressufficient output, power of the fuel cell and prevents deteriorationthereof, coping with the changing output characteristic thereof.

1. A power generation control system comprising: a fuel cell forgenerating power from fuel gas and oxidant gas fed thereto; a targetpower provider for providing a target power for the fuel cell; adetector for detecting output power from the fuel cell, the detectordetecting actual output voltage of the fuel cell; and a controllercomprising a target current computing unit which calculates a targetcurrent at the target power directly from a nominal power-currentcharacteristic obtained from a nominal output characteristic of the fuelcell, the nominal output characteristic corresponding to a referenceoutput characteristic; and a command output power computing unit whichcalculates a command output power of the fuel cell from the product ofthe target current and the actual output voltage.
 2. The powergeneration control system according to claim 1, further comprising: agas control system for controlling pressure and flow rate of therespective fuel gas and oxidant gas, wherein the controller furthercomprises a target gas operation point computing unit which calculates atarget gas operation point of the fuel gas and the oxidant gas at thetarget current based on a gas operation point characteristic whichprovides pressure and flow rate of the respective fuel gas and oxidantgas for an output current of the fuel cell, and an output characteristiclearning unit which learns an actual output characteristic of the fuelcell based on the output power thereof detected by the detector, andcorrects the reference output characteristic of the fuel cell based onthe learned actual output characteristic thereof, and wherein the gascontrol system controls the pressure and flow rate of the respectivefuel gas and oxidant gas based on the target gas operation pointcalculated by the target gas operation point computing unit, and whereinthe target current computing unit creates a revised power-currentcharacteristic based on the reference output characteristic of the fuelcell corrected by the output characteristic learning unit, and whereinthe target current computing unit calculates the target current at thetarget power based on the revised power-current characteristic.
 3. Thepower generation control system according to claim 1, furthercomprising: a gas control system for controlling pressure and flow rateof the respective fuel gas and oxidant gas, wherein the controllerfurther comprises a target gas operation point computing unit whichcalculates a target gas operation point of the fuel gas and the oxidantgas at the target current based on a gas operation point characteristicwhich provides pressure and flow rate of the respective fuel gas andoxidant gas for an output current of the fuel cell, and an outputcharacteristic learning unit which learns an actual outputcharacteristic of the fuel cell based on the output power thereofdetected by the detector, and corrects the reference outputcharacteristic of the fuel cell based on the learned actual outputcharacteristic thereof, and wherein the gas control system controls thepressure and flow rate of the respective fuel gas and oxidant gas basedon the target gas operation point calculated by the target gas operationpoint computing unit, and wherein the target gas operation pointcomputing unit revises the gas operation point characteristic based onthe reference output characteristic of the fuel cell corrected by theoutput characteristic learning unit.
 4. The power generation controlsystem according to claim 2, wherein the detector detects actual outputcurrent of the fuel cell in addition to the actual output voltage of thefuel cell, and wherein the output characteristic learning unit learnsthe actual output characteristic of the fuel cell based on the actualoutput current and the actual output voltage detected by the detector.5. The power generation control system according to claim 4, wherein theoutput characteristic learning unit collects actual output currents andactual output voltages of the fuel cell detected by the detector tocorrect the reference output characteristic of the fuel cell.
 6. Thepower generation control system according to claim 4, wherein the outputcharacteristic learning unit learns the actual output characteristic ofthe fuel cell based on the actual output currents and the actual outputvoltages of the fuel cell detected by the detector during apredetermined period.
 7. The power generation control system accordingto claim 2, further comprising: a thermometer for measuring an actualtemperature of the fuel cell, wherein the output characteristic learningunit has a plurality of pieces of output characteristic data for varioustemperatures of the fuel cell, and corrects the reference outputcharacteristic based on the measured actual temperatures of the fuelcell.
 8. The power generation control system according to claim 2,wherein the target power provider calculates target power by taking intoaccount power consumption of an auxiliary equipment for power generationof the fuel cell, and when the power-current characteristic of thetarget current computing unit or the gas operation point characteristicof the target gas operation point computing unit are corrected, acurrent-auxiliary power consumption characteristic, which provides powerconsumption of the auxiliary equipment for an output current of the fuelcell, are corrected based on the reference output characteristic of thefuel cell corrected by the output characteristic learning unit.
 9. Amethod of controlling power generation of a fuel cell, comprising:receiving target power for the fuel cell; detecting an output power fromthe fuel cell, and detecting an actual output voltage of the fuel cell;calculating a target current at the target power directly from a nominalpower-current characteristic obtained from a nominal outputcharacteristic of the fuel cell; and calculating a command output powerfor the fuel cell from the product of the target current and the actualoutput voltage.
 10. The method according to claim 9, further comprising:controlling pressure and flow rate of a fuel gas and an oxidant gas;calculating a target gas operation point of the fuel gas and the oxidantgas at a target current based on a gas operation point characteristicwhich provides pressure and flow rate of the respective fuel gas andoxidant gas for an output current of the fuel cell; learning an actualoutput characteristic of the fuel cell based on an output power thereofdetected by a detector, and correcting a reference output characteristicof the fuel cell based on the learned actual output characteristicthereof; controlling the pressure and flow rate of the respective fuelgas and oxidant gas based on the target gas operation point calculatedin the calculating a target gas operation point step; creating a revisedpower-current characteristic based on the reference outputcharacteristic of the fuel cell corrected by the learning an actualoutput characteristic step; and calculating the target current at atarget power based on the revised power-current characteristic.
 11. Themethod according to claim 9, further comprising: controlling pressureand flow rate of a fuel gas and an oxidant gas; calculating a target gasoperation point of the fuel gas and the oxidant gas at a target currentbased on a gas operation point characteristic which provides pressureand flow rate of the respective fuel gas and oxidant gas for an outputcurrent of the fuel cell; learning an actual output characteristic ofthe fuel cell based on an output power thereof detected by a detector,and correcting a reference output characteristic of the fuel cell basedon the learned actual output characteristic thereof controlling apressure and flow rate of the respective fuel gas and oxidant gas basedon the target gas operation point calculated in the calculating a targetgas operation point step; and revising the gas operation pointcharacteristic based on a reference output characteristic of the fuelcell corrected in the learning step.
 12. The method according to claim10, wherein the detector detects actual output current of the fuel cellin addition to an actual output voltage of the fuel cell, and thelearning an actual output characteristic step further comprises learningthe actual output characteristic of the fuel cell based on the actualoutput current and the actual output voltage detected by the detector.13. The method according to claim 12, wherein the learning an actualoutput characteristic step further comprises collecting actual outputcurrents and actual output voltages of the fuel cell detected by thedetector to correct the reference output characteristic of the fuelcell.
 14. The method according to claim 12, wherein the learning anactual output characteristic step further comprises learning the actualoutput characteristic of the fuel cell based on the actual outputcurrents and the actual output voltages of the fuel cell detected by thedetector during a predetermined period.
 15. The method according toclaim 10, further comprising: measuring an actual temperature of thefuel cell, wherein the learning an actual output characteristic stepfurther comprises analyzing a plurality of pieces of outputcharacteristic data for various temperatures of the fuel cell, andcorrecting the reference output characteristic based on the measuredactual temperatures of the fuel cell.
 16. The method according to claim10, wherein the step of calculating the target current calculates targetpower by taking into account power consumption of an auxiliary equipmentfor power generation of the fuel cell, and when a power-currentcharacteristic or the gas operation point characteristic are corrected,a current-auxiliary power consumption characteristic, which providespower consumption of the auxiliary equipment for an output current ofthe fuel cell, is corrected based on the reference output characteristicof the fuel cell corrected by the learning an actual outputcharacteristic step.